Are There Differences in the Cranial Base of Humans and Apes?

Purpose: Differences in skull-base angles between humans, other hominid species and apes might account for the ability of humans to develop complex speech. This study compared midline skull base angles, and angles related to insertion of skull base musculature between these species.

Methods: 126 human adult, 29 adolescent, 19 children, and 13 fetus skulls were compared to 32 ape and a subset of non-human antiquity hominid casts of skulls (13). Cranial base measurements were taken using an eMicroscribe 3d G2 digitizer. Midline and muscle insertion measurements were obtained.

Results: There were statistical differences in both the midline angles of the skull base (humans, 119^o; apes, 130^o) and in the Skull base angles related to points of muscle insertion (humans, 113^o; apes, 124^o), with humans exhibiting a more acute angle than the apes and other non-human hominids. There were no differences between human adults and children CONCLUSION: Acute angle differentiation of the midline skull base between humans and apes was confirmed with an alternate measurement method. Whether these angular differences are the primary reason for the lower position of the larynx in humans and the potential for more complex speech is still in debate.